The HDMI™ (High-Definition Multimedia Interface) standard, of the HDMI consortium, is a digital interface for audio and video signals. HDMI-CEC refers to an HDMI device that supports CEC (Consumer Electronics Control). HDMI-CEC devices enable a user to manage a plurality of sources connected via HDMI with no special programming needed and to run operations such as ‘one touch play’. Using HDMI-CEC, the user may, for example, use one remote control to turn on the TV, DVD, and receiver at the same time, and to adjust the system volume using one button.
The HDMI-CEC protocol uses a one-wire shared bus that includes automatic mechanisms for logical address allocation based on product type, arbitration, retransmission, broadcasting, and switching control. Operation code (opcode) supports both device specific and general features. CEC devices have both physical and logical addresses. Normally, upon hot-plugging, each CEC source device obtains a physical address by reading the EDID of the display device to which it is attached.
In some embodiments, an HDMI-CEC message, shortly referred to as “CEC message”, includes the following CEC blocks: a special start ‘bit’, a header block containing source and destination addresses, a first data block containing optional opcode, and a second data block containing optional operands specific to the opcode. The maximum CEC message size (header block plus opcode block plus operand blocks) is 16*10 bits. Each CEC block includes 8 bits of data, one End-Of-Message (EOM) bit, and one acknowledge (ACK) bit transmitted by the receiver. A CEC message includes a series of CEC blocks wherein only the EOM bit of the last block in the message is on. Each CEC message starts with a block having 4 bits of source address (also referred to as nibble), 4 bits of destination address, an EOM bit, and an ACK bit. A polling message includes the same source and destination addresses with the EOM bit on.
CEC includes an option for customized commands. This enables different vendors to create CEC based networks between products of the specific vendor. Examples of such modified CEC base networks include: Anynet (Samsung), Aquos Link (Sharp), BRAVIA Theatre Sync (Sony), Regza Link (Toshiba), RIHD (Onkyo), Simplink (LG), Viera Link/EZ-Sync (Panasonic/JVC), Easylink (Philips) and NetCommand for HDMI (Mitsubishi).